Through air drying has become the technology of preference for making one-ply absorbent paper for many manufacturers who build new absorbent paper machines as, on balance, through air drying (xe2x80x9cTADxe2x80x9d) offers many economic benefits as compared to the older technique of conventional wet-pressing (xe2x80x9cCWPxe2x80x9d). With through air drying, it is possible to produce a single-ply absorbent paper in the form of a tissue with good initial softness and bulk as it leaves the absorbent paper machine.
In the older wet pressing method, to produce a premium quality printed, absorbent paper, it has normally been preferred to combine two plies by embossing them together. In this way, the rougher air-side surfaces of each ply may be joined to each other and thereby concealed within the sheet. However, producing two-ply products, even on state of the art CWP machines, lowers paper machine productivity by about 20% as compared to a one-ply product. In addition, there may be a substantial cost penalty involved in the production of two-ply products because the parent rolls of each ply are not always of the same length, and a break in either of the single plies forces the operation to be shut down until it can be remedied. Also, it is not normally economic to convert older CWP tissue machines to TAD. But even though through air drying has often been preferred for new machines, conventional wet pressing is not without its advantages as well. Water may normally be removed from a cellulosic web at lower energy cost by mechanical means such as by overall compaction than by drying using hot air.
What has been needed in the art is a method of making a premium quality printed single-ply absorbent paper using conventional wet pressing having a high bulk and excellent softness attributes. In this way advantages of each technology could be combined so older CWP machines can be used to produce high quality printed single ply absorbent paper products in the form of bathroom tissue, facial tissue, and napkin at a cost which is far lower than that associated with producing two-ply absorbent paper. Two-ply absorbent papers are normally printed on the top ply. Any ink migration through the top ply (strikethrough) is hidden by the bottom ply, which also provides a barrier to further ink migration. In printing single-ply absorbent papers, it is important to prevent or minimize ink strikethrough onto process equipment, which can compromise process efficiency.
Among the more significant barriers to the production of printed single-ply CWP absorbent paper have been the generally low softness, thinness and the extreme sidedness of single-ply webs and their inability to hold the ink without having undesirable ink migration which renders the prior art one-ply products unprintable. An absorbent product""s softness can be increased by lowering its strength, as it is known that softness and strength are inversely related. However, a product having very low strength will present difficulties in manufacturing and will be rejected by consumers as it will not hold up in use. Use of premium, low coarseness fibers, such as eucalyptus, and stratification of the furnish so that the premium softness fibers are on the outer layers of the tissue is another way of addressing the low softness of CWP products; however this solution is expensive to apply, both in terms of equipment and ongoing fiber costs. In any case, neither of these schemes addresses the problem of thinness of the web and the resulting unprintability of the absorbent paper product. TAD processes employing fiber stratification can produce a nice, soft, bulky sheet having adequate strength and good similarity of the surface texture on the front of the sheet as compared to the back. Having the same texture on front and back is considered to be quite desirable in these products or, more precisely, having differing texture is generally considered quite undesirable. Because of the deficiencies mentioned above, many single-ply CWP products currently found in the marketplace are typically low end products which cannot be printed. These products often are considered deficient in thickness, softness, and exhibit excessive two sidedness. Accordingly, these products have had rather low consumer acceptance and are typically used in xe2x80x9caway from homexe2x80x9d applications in which the person buying the tissue is not the user. It should be not that to date there are no commercially printed one-ply CWP absorbent paper products.
We have found that we can produce a soft, printed, high basis weight, high strength CWP bathroom tissue, facial tissue, and napkins with low sidedness having a serpentine configuration by judicious combination of several techniques as described herein. Basically, these techniques fall into five categories: (i) providing a web having a basis weight of at least 12.5 pounds for each 3000 square foot ream; (ii) optionally adding to the web a controlled amount of a temporary wet strength agent and softener/debonder; (iii) low angle, high percent crepe, high adhesion creping giving the product low stiffness and a high stretch; (iv) optionally embossing the tissue; and (v) printing one or both sides of the absorbent paper product either before or after embossing. By various combinations of these techniques as described, taught, and exemplified herein, it is possible to almost xe2x80x9cdial inxe2x80x9d for the printed absorbent paper the required degree of softness, strength, and sidedness depending upon the desired goals. The use of softeners having a melting range of about 1xc2x0-40xc2x0 C. and being dispersible at a temperature of about 1xc2x0-100xc2x0 C. suitably 1xc2x0-40xc2x0 C. preferably 20xc2x0-25xc2x0 C. further improves the properties of the novel printed, one-ply absorbent paper product having a serpentine configuration.
The confirmation that our products have a very low printed sidedness was obtained by printing the Yankee side and the air side of the absorbent paper and comparing the differences. Surprisingly, on visual inspection, no differences could be ascertained and by the use of a spectrodensitometer, the total color difference (xcex94E) values supported the visual observation.
Samples were measured with an X-Rite 938 spectrodensitometer. A solid tone was measured for L*C*Hxc2x0 color space coordinates and xcex94Ecmc using a 4 mm aperture, D65 light source, 10xc2x0 standard observer, 2:1:1 factor setting. As described in the X-Rite Color Guide and Glossary, L*C*Hxc2x0 is a three-dimensional cylindrical representation of color, where L* depicts Lightness, C* depicts Chroma (saturation), and Hxc2x0 depicts Hue angle. The X-Rite 938 Operation Manual defines xcex94Ecmc as a single numeric value that expresses total color difference between a sample and a standard. CMC tolerancing is a modification of the L*C*Hxc2x0, providing better agreement between visual assessment and instrumentally measured color difference. The CMC calculation mathematically defines an ellipsoid around the standard color with semi-axis corresponding to hue, chroma, and lightness and allows for a user defined acceptance level. An average of three measurements were reported. Differences in total color (xcex94E) were used to quantify similarity or differences in print appearance between the samples as a logical means to express relationships between the three-dimensional space of lightness, chroma, and hue angle. At an xcex94Ecmc value of xe2x89xa61.0, the standard observer would not detect differences in appearance between samples and at xcex94Exe2x89xa62.0, the differences would be very low. At xcex94Exe2x89xa73.0 differences would be readily observable. The backing ply was also measured for ink transfer using the same X-Rite settings. The amount of ink strikethrough on the backing ply was compared to white, non-print areas. Larger xcex94E levels indicate a greater total level of strikethrough. Relative differences between samples of xcex94Ecmcxe2x89xa61.0 indicate similar levels of strikethrough.
1. Field of the Invention
The present invention is directed to a printed, soft, strong in use, bulky single-ply absorbent paper product having a serpentine configuration and a low sidedness and processes for the manufacture of such paper. More particularly, this invention is directed to a printed, soft, strong-in-use, bulky, single-ply bathroom tissue, facial tissue, and napkin having a low printed sidedness, suitably a value of xcex94E of less than 2, preferably less than 1 in addition to a low surface sidedness parameter of less than 0.3.
2. Description of Background Art
Paper is generally manufactured by suspending cellulosic fiber of appropriate geometric dimensions in an aqueous medium and then removing most of the liquid. The paper derives some of its structural integrity from the mechanical arrangement of the cellulosic fibers in the web, but most by far of the paper""s strength is derived from hydrogen bonding which links the cellulosic fibers to one another. With paper intended for use as bathroom tissue, facial tissue or napkin, the degree of strength imparted by this inter-fiber bonding, while necessary to the utility of the product, can result in a lack of perceived softness that is inimical to consumer acceptance. One common method of increasing the perceived softness of bathroom tissue, facial tissue and napkin is to crepe the paper. Creping is generally effected by fixing the cellulosic web to a Yankee drum thermal drying means with an adhesive/release agent combination and then scraping the web off the Yankee by means of a creping blade. Creping, by breaking a significant number of inter-fiber bonds adds to and increases the perceived softness of resulting bathroom tissue product.
Another method of increasing a web""s softness is through the addition of chemical softening and debonding agents. Compounds such as quaternary amines that function as debonding agents are often incorporated into the paper web. These cationic quaternary amines can be added to the initial fibrous slurry from which the paper web is subsequently made. Alternatively, the chemical debonding agent may be sprayed onto the cellulosic web after it is formed but before it is dried.
One-ply bathroom tissue, facial tissue and napkin, generally suffers from the problem of thinness and therefore unprintability, lack of softness, and also xe2x80x9csidedness.xe2x80x9d Sidedness is introduced into the sheet during the manufacturing process. The side of the sheet that was adhered to the Yankee and creped off, i.e., the Yankee side, is generally softer than the xe2x80x9cairxe2x80x9d side of the sheet. This two-sidedness is seen both in sheets that have been pressed to remove water and in unpressed sheets that have been subjected to vacuum and hot air (through-drying) prior to being adhered to the crepe dryer. The sidedness is present even after treatment with a softener. A premium one-ply bathroom tissue, facial tissue or napkin, should not only have a high overall softness level, but should also exhibit softness of each side approaching the softness of the other.
The most pertinent prior art patents will be discussed but, in our view, none of them can be fairly said to apply to the printed, one-ply, absorbent paper of this invention which exhibits high thickness, soft, strong and low sidedness attributes. In U.S. Pat. No. 5,164,045, Awofeso et al. disclose a soft, high bulk tissue. However, production of this product requires stratified foam forming and a furnish that contains a substantial amount of anfractuous and mechanical bulking fibers, none of which are necessary to practice the present invention; also, the paper products of U.S. Pat. No. 5,164,045 cannot be printed.
In U.S. Pat. No. 5,695,607, Oriaran, et al. disclose a low sidedness product, but the tissue is not printed. In addition, production of this product requires such strategies as fiber and/or chemical stratification that have been found unnecessary to produce the product of the present invention. Dunning et al., U.S. Pat. No. 4,166,001, discloses a double creped three-layered product having a weak middle layer. The Dunning product does not suggest the printed one-ply premium soft absorbent paper products of this invention having a serpentine configuration and also having a low printability sidedness (xcex94E).
The foregoing prior art references do not disclose or suggest a printed, high-softness, strong one-ply absorbent paper product in the form of a bathroom tissue, facial tissue, or napkin having serpentine configuration and low sidedness and having a total specific tensile strength of no more than 200 grams per three inches per pound per 3000 square foot ream, optionally a cross direction wet tensile strength of at least 2.75 grams per three inches per pound per 3000 square foot ream, a specific geometric mean tensile stiffness of 0.5 to 3.2 grams per inch per percent strain per pound per 3,000 square foot ream, a GM friction deviation of no more than 0.25 and a sidedness parameter less than 0.3.
The novel premium quality printed, high-softness, single-ply absorbent paper product having a serpentine configuration and a very low xe2x80x9csidednessxe2x80x9d including low printability sidedness (xcex94E) along with excellent softness, coupled with strength is advantageously obtained by using a combination of five processing steps.
Suitably, the printed premium softness, strong, low sidedness absorbent paper in the form of a bathroom tissue, facial tissue, or napkin has been prepared by utilizing techniques falling into five categories: (i) providing a web having basis weight of at least 12.5 pounds for each 3000 square foot ream; (ii) optionally adding to the web or to the furnish controlled amounts of a temporary wet strength agent and adding a softener/debonder preferably a softener dispersible in water at a temperature of about 1xc2x0-100xc2x0 C. suitably 1xc2x0-40xc2x0 C. advantageously 20xc2x0-25xc2x0 C. Advantageously the softener should have a melting point below 40xc2x0 C.; (iii) low angle, high adhesion creping using suitable high strength nitrogen containing organic adhesives and a crepe angle of less than 85 degrees, the relative speeds of the Yankee dryer and reel being controlled to produce a product having a final product MD stretch of at least 15%; and (iv) optionally embossing the one-ply absorbent paper product preferably between matted emboss rolls; and (v) printing the paper product on one or both sides either before or after embossing. The furnish may include a mixture of softwood, hardwood, and recycled fiber. The premium softness and strong, single-ply, absorbent paper product having low sidedness may be suitably obtained from a homogenous former or from two-layer, three-layer, or multi-layer stratified formers.
Further advantages of the invention will be set forth in part in the description which follows. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention as embodied and broadly described herein, there is disclosed:
A method of making a printed, high-softness, high-basis weight, single-ply absorbent paper product having a serpentine configuration. This paper product is suitably in the form of a bathroom tissue, facial tissue, or napkin. The absorbent printed paper product is prepared by:
(a) providing a fibrous pulp of papermaking fibers;
(b) forming a nascent web from said pulp, wherein said web has a basis weight of at least about 12.5 lbs./3000 sq. ft. ream;
(c) optimally including in said web at least about 3 lbs./ton of a temporary wet strength agent and up to 10 lbs./ton of a nitrogen containing softener; optionally a cationic nitrogen containing softener; dispersible in water at a temperature of about 1xc2x0-100xc2x0 C. suitably 1xc2x0-40xc2x0 C. advantageously 20xc2x0-25xc2x0 C., advantageously the softener has a melting point below 40xc2x0 C.;
(d) dewatering said web;
(e) adhering said web to a Yankee dryer;
(f) creping said web from said Yankee dryer using a creping angle of less than 85 degrees, wherein the relative speeds between said Yankee dryer and the take-up reel is controlled to produce a final product MD stretch of at least about 15%;
(g) optionally calendering said web;
(h) optionally embossing said web preferably between matted emboss rolls; and
(i) printing one or both sides of the web prior to or after embossing using either the rotogravure or flexographic printing process; and
(j) forming a single-ply web wherein steps (a)-(f) and (i) and optionally steps (g) and (h) are controlled to result in a single-ply absorbent paper product in the form of a bathroom tissue, facial tissue, or napkin having a serpentine configuration and a total specific tensile strength of no more than 200 grams per three inches per pound per 3,000 square foot ream, suitably no more than 150 grams per three inches per pound per 3,000 square foot ream, preferably no more than 75 grams per three inches per pound per 3,000 square foot ream, a cross direction wet tensile strength of at least 2.7 grams per three inches per pound per ream, a specific geometric ream tensile stiffness of between 0.5 and 3.2 grams per inch per percent strain per pound per 3,000 square foot ream, a GM friction deviation of no more than 0.25 and a sidedness parameter less than 0.3 usually in the range of about 0.180 to about 0.250 and suitably the printed side has a xcex94E value of less than 2, preferably less than 1, when the total specific tensile strength does not exceed 75 grams per three inches per pound per 3,000 square foot ream.
To summarize at a total specific tensile strength of about 200 grams per 3 inches or less per 3,000 square foot ream, the cross direction specific wet tensile strength is about 20 grams or less per 3,000 square foot ream, the ratio of MD tensile to CD tensile is between 1.25 and 2.75. The specific geometric mean tensile strength is 3.2 or less grams per inch per percent strain per pound per 3000 square foot ream. The friction deviation is less than 0.25 and the sidedness parameter is less than 0.30. At a total specific tensile strength of about 150 grams per 3 inches or less per 3000 square foot ream the cross direction specific wet tensile strength is about 15 grams or less per 3000 square foot ream, the ratio of MD tensile to CD tensile is between 1.25 and 2.75. The specific geometric ream tensile strength is 2.4 or less grams per inch per percent strain per pound per 3000 square foot ream. The friction deviation is less than 0.25 and the sidedness parameter is less than 0.30. When the absorbent paper in the form of a bathroom tissue, facial tissue or napkin exhibits a total specific tensile strength between 40 and 75 grams per 3 inches per 3000 square foot ream, it has a cross direction specific wet tensile strength of between 2.75 and 7.5 grams per 3 inches per pound per 3000 square foot ream, and its specific geometric mean tensile stiffness is between 0.5 and 1.2 grams per inch per percent strain per pound per 3000 square foot ream and its friction deviation is less than 0.225; and the tissue has sidedness parameter of less than 0.275.
In one embodiment of this invention, the one-ply, printed, absorbent paper product may be embossed with a pattern that includes a first set of bosses which resemble stitches, hereinafter referred to as stitch-shaped bosses, and at least one second set of bosses which are referred to as signature bosses. Signature bosses may be made up of any emboss design and are often a design which is related by consumer perception to the particular manufacturer of the tissue.
In another aspect of the present invention, a paper product is embossed with a wavy lattice structure which forms polygonal cells. These polygonal cells may be diamonds, hexagons, octagons, or other readily recognizable shapes. In one preferred embodiment of the present invention, each cell is filled with a signature boss pattern. More preferably, the cells are alternatively filled with at least two different signature emboss patterns.
In another preferred embodiment, one of the signature emboss patterns is made up of concentrically arranged elements. These elements can include like elements for example, a large circle around a smaller circle, or differing elements, for example a larger circle around a smaller heart. In a most preferred embodiment of the present invention, at least one of the signature emboss patterns are concentrically arranged hearts as can be seen in FIG. 6. Again, in a most preferred embodiment, another signature emboss element is a flower.
These one-ply absorbent papers in the form of a bathroom tissue, facial tissue, or napkin can suitably be printed on the Yankee or air side prior to or after embossing. The product can suitably be printed on both sides. In some applications the one-ply absorbent paper is not embossed but designs are printed on it.
The printed, one-ply absorbent paper of this invention in the form of a bathroom tissue, facial tissue, or napkin has higher softness and strength parameters than prior art one-ply absorbent paper products and the embossed one-ply tissue product of the present invention has superior attributes than prior art one-ply embossed tissue products. The use of concentrically arranged emboss elements in one of the signature emboss patterns adds to the puffiness effects realized in the appearance of the paper product tissue. The puffiness associated with this arrangement is the result not only of appearance but also of an actual raising of the tissue upward.